I. Field of the Invention
The invention relates to the implantation and placement of cardiac leads used in combination with cardiac rhythm management devices, e.g., heart pacemakers or defibrillators, to monitor and control the rhythm of the heart. This invention is more particularly directed toward a guidewire/pacing lead configuration adapted to assist in the implantation and placement of a cardiac lead having one or more electrodes that are to reside in the distal branches of the coronary venous system, the great cardiac vein, or coronary sinus. The invention also encompasses the use of a guide catheter along with a guidewire and removal wire configurations useful in removing guide catheters without dislodging the implanted leads.
II. Discussion of the Prior Art
Placement of cardiac leads in the distal branches of the coronary venous system, the great cardiac vein, or the coronary sinus is a difficult task. Often when deploying the lead there comes a point at which the lead cannot be advanced further into the vascular system using standard techniques and equipment. All too often this point is not the optimal position for the lead""s electrode, either for sensing cardiac electrical activity or delivering pacing therapy to the heart.
There are several reasons which make proper placement of the lead difficult. These include (1) friction between the vasculature and the lead; (2) partial obstruction of the vasculature; (3) unusually shaped bifurcations in the vasculature; and (4) accumulative friction between lead, guide catheter and guidewire. Prior efforts to resolve such problems included the use of a stiffer guidewire. While stiffer guidewires offer additional support, they may impede advancement due to their relative size with respect to the lumen of the lead. Additionally, when proper placement of the lead is achieved, problems arise during guide catheter or guidewire extraction. All too often, the act of extracting the guide catheter and/or guidewire causes the lead to be dislodged from the implanted position. Standard guidewires and stylets are not suitable for maintaining position while the guide catheter is removed due to insufficient stiffness, lack of appropriate force transmission features, and friction between the guidewire and lumen wall of the coronary vein lead. A means must be provided which will hold the lead and its corresponding electrodes in place while allowing the guide catheter and guidewire to be removed.
The present invention is deemed to be an improvement over conventional prior art guidewires. It is more effective in properly placing the lead and it is also less likely to cause a properly placed lead to become dislodged during extraction of the guide catheter and the guidewire itself.
In cases where the over-the-wire lead is to be implanted without the aid of a guide catheter, the guidewire may be of a uniform stiffness along its length except at a distal end portion where there is attached a floppy segment comprising a coiled wire helix having a very thin, flexible core member extending through the center of the helix and with the distal end of the core wire affixed to an atraumatic tip. The stiffness of the guidewire is designed to be less than the stiffness of the lead with which it is used. The lead is of the type having an elongated, flexible, polymeric lead body with a lumen extending the full length thereof from a proximal end to a distal end and of a cross-section allowing the guidewire to extend therethrough as the lead body is advanced over the guidewire in placing the lead""s electrode(s) at a desired location within the patient""s vasculature.
Because the lead has a somewhat greater stiffness property than its associated guidewire, there are greater frictional forces between the lead and the vessel in which it is placed than between the guidewire and the wall of the lead body defining the lead""s lumen. Hence, the guidewire can be removed from the lead without dragging the lead with it.
In instances where a guide catheter is first advanced through a blood vessel and into the ostium of the coronary sinus before the guidewire is inserted and the lead advanced over the guidewire, it may become necessary to utilize a removal wire to hold the lead against movement as the surrounding guide catheter is removed subsequent to removal of the guidewire. The removal wire includes an element for engaging the lead and holding it stationary as the guide catheter is stripped free of the pacing lead body.
In accordance with a second embodiment of the present invention, there is provided a guidewire comprised of at least three zones. Each zone differs from the other two in terms of its stiffness and flexibility. Each zone also has geometric characteristics which assist in proper placement of the lead and further assist in preventing dislodgement of the lead as the guide catheter is extracted and as the guidewire itself is extracted.
Specifically, the first and most distal zone is intended to be very floppy to prevent trauma to the surrounding vessel walls when the guidewire is being advanced beyond the distal end of a guide catheter when deploying a coronary vein lead. This distal zone may include a spiral wound portion surrounding a thin, solid ribbon core and a spherical tip. The second zone is relatively more stiff than its adjacent distal section and may comprise a solid wire or spiral wound wire having a cross-sectional diameter that does not exceed the cross-sectional diameter of the first zone. The second and most proximal zone is preferably of a larger diameter and is somewhat stiffer than the first zone but not as stiff and flexible as the lead body in which it is inserted. The second zone comprises a wire or hypo tube which can be manipulated to apply advancement forces during deployment of the lead and stabilizing forces to a lead during extraction of the guide catheter. A diametric transition between the first and second zones is abrupt and ideally corresponds to a matching feature in the lead so that this transition is the point where most of the advancement forces and counter forces are transmitted to the lead.
In a third embodiment, a removal wire is provided which has a squared end for engaging a portion of the lead to hold it in place during guide catheter removal. The guide catheter easily disengages from the lead for withdrawal of the removal wire.
In yet another embodiment a three zone removal wire is used which extends beyond the length of the guide catheter, but does not exit the lead to frictionally hold the lead in place while removing the guide catheter.
In still another embodiment the three zone removal wire is provided with a temporary locking means to hold the lead in place while removing the guide catheter. The temporary locking means can be proximal, distal or both. The temporary locking means can also be along the length of the removal wire or in the lumen of the lead.
In a further embodiment the removal wire with the temporary locking means can be modified to have only one zone.
Other improvements also exist. For example, the improved guidewire (or portions thereof) can be provided with a hydrophilic coating to produce a highly lubricious surface. The presence of such a surface reduces friction between the lumen wall of the lead and the guidewire thereby reducing the risk that the lead will be dislodged during extraction of the guidewire.